To deal with the Harmonic Current Regulation (IEC610003-2) and the Appliance/commodity harmonic current suppressing guideline, a switching power source apparatus that has a power factor improving function is included in an AC adapter, an office automation equipment, or various commercial-devices. Concerning these AC adapters, office automation equipments, and various commercial-devices, also, miniaturization, lower costs, and saving of energy is desired. These kinds of switching power source apparatuses are disclosed in for example the below documents.
Document 1: Examined Japanese Patent Application KOKOKU Publication No. H7-57095
Document 2: Unexamined Japanese Patent Application KOKAI Publication No. H6-121535
In Examined Japanese Patent Application KOKOKU Publication No. H7-57095, a drive power source winding is provided in a transformer of a DC/DC converter, for deleting the constant-voltage circuit added to the drive power source, by stabilizing the drive voltage of the control circuit of the power factor improvement circuit, without receiving effect of the load. In the art of Examined Japanese Patent Application KOKOKU Publication No. H7-57095, the DC voltage generated by rectifying and smoothing the output voltage of the drive power source winding, is applied to a voltage dividing point of the voltage resistance provided in between the DC inputs, to generate drive voltages of the power factor improvement circuit and the DC/DC conversion circuit.
In Unexamined Japanese Patent Application KOKAI Publication No. H6-121535, a starting circuit that supplies drive power to both the DC/DC conversion control circuit and the power factor improvement circuit control circuit by a winding wounded around the transformer of the DC/DC converter, starts operation of the DC/DC converter when the power factor improvement circuit starts, and starts operation of the power factor improvement circuit thereafter.
The present invention proposes a power-saving starting method, a starting circuit, and an apparatus that accurately starts, from another aspect than the art disclosed in the above documents.
FIG. 7 is an example of a structural diagram of an outline of a conventional switching device and a starting circuit thereof.
This switching power source apparatus comprises a rectifier circuit 2 that full-wave rectifies the voltage from an AC power source 1, a power factor improvement circuit 10 that constitutes an AC/DC conversion circuit together with the rectifier circuit 2, and a DC/DC conversion circuit 20 that is connected to the output side of the power factor improvement circuit 10, and control units 19 and 29 that control the switching of the power factor improvement circuit 10 and the DC/DC conversion circuit 20.
The starting circuit of the switching power source apparatus comprises a backup capacitor 31 and an energy supply circuit 32 that are built into the DC/DC conversion circuit 20. The energy supply circuit 32 comprises a dividing voltage resistances that collects energy supplied from the power source 1, and generates drive voltage of the control units 19 and 29 with that energy.
Next, operation of the starting circuit and switching power source apparatus shown in FIG. 7 will be described.
FIGS. 8A to 8F are timing charts for describing operation of the switching power source apparatus.
When the AC power source 1 (FIG. 8(A)) is applied at a time t0, the rectifier circuit 2 starts total-wave rectifying of the AC voltage, and outputs the rectified rectifier voltage to a coil 12 in the power factor improvement circuit 10. The diode 14 whose anode is connected to the coil 12, and the capacitor that is connected to the cathode of the diode 14, carries out rectifying and smoothing of the rectifier voltage. At the point that the AC power source 1 is applied, an energy supply circuit 32 functions to pass a current from the capacitor 16, and charges the backup capacitor 31.
By the charging current of the energy supply circuit 32, energy is accumulated in the backup capacitor 31, and charge voltage rises (FIG. 8(B)). When the charge voltage of the backup capacitor 31 becomes equal to or higher than a predetermined voltage, the control units 19 and 29 activate with the energy accumulated in the backup capacitor 31, and turn on at a time t1 (FIGS. 8(C), 8 (E)).
On the other hand, resistances 11a and 11b, in the power factor improvement circuit 10, that is connected serially in between the anode terminal and the cathode terminal of the rectifier circuit 2, divide the rectifier voltage to generate a voltage signal. The resistances 17a and 17b that are serially connected in between two electrodes of the capacitor 16, divide the charging voltage of the capacitor 16 to generate a voltage signal. The coil 18 that electromagnetically couples with the coil 12, generates a voltage signal when energy is emitted from the coil 12. The NMOSS transistor 13 whose drain is connected to the coil 12, passes a current that passes through the coil 12, when it is an on state, to the cathode terminal of the rectifier circuit 2, and the resistance 15 that is connected to the source of the NMOS transistor 13 generates a voltage signal that is proportional to that current. The voltage signals are supplied to the control unit 19.
The control unit 19 that turns on with the supplied energy, generates a control signal based on the voltage signal supplied from the power factor improvement circuit 10, and supplies the control signal to the gate of the NMOS transistor 13, to control on/off of the NMOS transistor 13. By turning the NMOS transistor 13 on, current is passed through, in the order of, coil 12, NMOS transistor 13, resistance 15, to the cathode terminal of the rectifier circuit 2, from the anode terminal of the rectifier circuit 2, and energy is accumulated in the coil 12. When the NMOS transistor 13 is turned off, the energy accumulated in the coil 12 and the energy output from the rectifier circuit 2 passes via the diode 14, and the capacitor 16 is charged. The NMOS transistor 13 is repeatedly turned on and off. The charging voltage of the capacitor 16 becomes a predetermined voltage raised from the output voltage of the rectifier circuit 2 (FIG. 8(D)). By the NMOS transistor 13 repeatedly being turned on and off, the current that intermittently flows through the coil 12 is controlled so that it matches with the phase of the rectifier voltage that the rectifier circuit 2 generates. Namely, power factor improving operation is carried out.
On the other hand, the output voltage detection circuit 25 in the DC/DC conversion circuit 20 supplies a voltage signal that indicates charging voltage of the capacitor 24, to the control unit 29. The control unit 29 that is turned on, by being supplied energy, repeatedly turns the NMOS transistor 22 on and off, so that the charging voltage of the capacitor 24 becomes a predetermined value, based on the voltage signal supplied from the output voltage detection circuit 25.
When the NMOS transistor 22 is turned on, a current from the capacitor 16 flows through the primary winding 21a of a transformer 21, and energy is accumulated in the primary winding 21a. When the NMOS transistor 22 is turned off, flyback energy that corresponds to the energy of the primary winding generates in the transformer 21 of a second winding 21b, and is charged to the capacitor 24 via the diode 23 (FIG. 8(F)).
When the NMOS transistor 22 is turned off, flyback energy also generates in the auxiliary winding 26, which electromagnetically couples with the primary winding 21a. The flyback energy is charged to the backup capacitor 31 via the diode 27. Therefore, energy supplied to the control units 19 and 29 do not exhaust.
In this way, after the power source 1 is applied, the backup capacitor 31 is charged by the energy supply circuit 32, and the operation of the control units 19 and 29 are started by the energy charged to the backup capacitor 31, so as to operate the power factor improvement circuit 10 and DC/DC conversion circuit 20, to supply a requested DC voltage to the load 70.
However, there are problems such as below, in the starting method and starting circuit of the conventional switching power source.
The control unit 19 and 20 are activated at the same time by the energy charged in the backup capacitor 31 operate. Therefore, because the backup capacitor 31 needs to supply energy that drives two control units 19 and 29, a large capacity is necessary, and the size of the backup capacitor 31 grew. This hinders miniaturization and low cost of starting circuits, and switching power source apparatuses that have them built in.
Also, because the capacity of the backup capacitor 31 is large, the time needed to start the operation of the controls units 19 and 29 become longer. To solve this, if charging current that the energy supply circuit 32 passes through to the backup capacitor 31 is increased, there is a problem that the energy supply circuit 32 generates heat.
Further, another significant problem is that by the variation in starting voltage of the control units 19 and 29, starting deficiency in that the operation of one control unit starts, but the other does not, and the output voltage of the power factor improvement circuit 10 or the DC/DC conversion circuit 20 dropping by the power being taken up by the control unit that starts first, occurring by the starting time of the control units not matching.
Namely, it can not be determined which of the power factor improvement circuit 10 and the DC/DC conversion circuit 20 will start first, and even if they started at the same time, as shown in FIG. 8(D), rising of the power factor improvement circuit 10 is slow compared to the DC/DC conversion circuit 20. If the DC/DC conversion circuit 20 rapidly rises and flows a large current, before the output voltage of the power factor improvement circuit 10 becomes an adequate voltage, the output voltage of the power factor improvement circuit 10 further drops. As a result, the input voltage of the DC/DC conversion circuit 20 is not sufficient, and adequate energy can not be supplied to the output side. This leads to rising of the output voltage becoming longer, intermittent operation generating by the input voltage reducing, and rising time of the output voltage further becoming longer, and rising of the auxiliary power source built into the DC/DC conversion circuit 20 becoming late. To solve this, it is necessary to pass a large current to the dividing voltage resistance for starting, and make the capacity of the backup capacitor 31 built in the DC/DC conversion circuit 20 larger.
The Unexamined Japanese Patent Application KOKAI Publication No. H6-121535 discloses a method for driving the DC/DC conversion circuit 20 first, and has the same problem, because it is started in a state where the input voltage of the DC/DC conversion circuit 20 is low.
The object of the present invention is to provide a power saving, method for starting an apparatus, a starting circuit of a power source apparatus or a power source apparatus, which starts accurately and rapidly, and can miniaturize the capacity of the backup capacitor.